1. Field of the Invention
The present invention relates to a method and a device for a wireless energy transmission.
2. Description of the Related Art
Wireless energy transmission may be used for transmitting energy inductively from a first device to a second device. The first device may include in particular a power supply and the second device may include a small electrical device having a battery or an accumulator. In order to charge the accumulator, the small electrical device is brought into a magnetic sphere of influence of the power supply and the energy transmission is started.
For the energy transmission, the power supply and the small electrical device may each include a coil, the coils being magnetically coupled to one another. With the aid of a transmitter coil, the power supply generates an alternating magnetic field, which the receiver converts back into an electric current with the aid of its receiver coil. This current may be subsequently fed to the accumulator via a charge controller.
It is possible for a magnetizable or electrically conductive object to enter the magnetic sphere of influence of the transmitter coil and become heated there in the alternating magnetic field due to eddy currents or core losses or hysteresis losses. The heating may be considerable, making it possible for a risk of accidents to emanate from the object.
The object may be detected, for example, by scanning an electrical parameter on the transmitter coil and comparing it with a predetermined threshold value. If the scanned value exceeds the threshold value, the presence of an object is inferred and the wireless transmission of energy is terminated. In order to also be able to detect a small object reliably, the comparison must occur at close tolerances. However, the danger then exists that another influence on the electrical parameter, for example, an aging effect, a system voltage fluctuation, or the only temporary presence of an object, will result in a termination of the transmission of energy. In particular, an uncontrolled transmission of energy caused by a user, such as is used for charging accumulators, may thus defeat its actual purpose.